Learning the lessons of flight AF447

During its investigation of AF447, there were some pilot/aircraft interface issues the BEA listed as sub-optimal, but it only proposes a specific solution for one of them.

The list includes:

  • The flight directors appeared and disappeared periodically from the primary flight display. It would be better, says the BEA, if they had been withdrawn completely
  • The electronic centralised aircraft monitor provided the crew with accurate information about symptoms of the problem, namely that the autopilot and autothrust had tripped out and the aircraft was in alternate flight control law, but it did not reveal the reason for these symptoms was the detection of unreliable airspeed inputs
  • The BEA observes that when the aircraft was flying in a stalled condition at less than 60kt (110km/h) indicated airspeed, the audible stall warning stopped, and as soon as the airspeed rose just above 60kt the stall warning re-started, potentially sending a message to a crew that was trying to reduce the angle of attack by pitching down that pushing the stick forward created a stalled condition. The system logic is that, below 60kt, the pitot-static system cannot provide reliable airspeed information, so the data cuts out and so does the stall warning. The BEA notes, however, that this anomaly occurs only when the aircraft had already entered what most aviators would consider an unthinkably extreme flight condition
  • An A330 crew is not provided with a read-out of angle-of-attack (AOA). AOA has a direct relationship with stall risk. On the other hand, the BEA notes, stall AOA reduces as the mach number increases, so there is no guarantee that an already overstressed crew would know which angle applied at their flight level, or take account of it. However the BEA recommends that the EASA and the FAA should consider requiring that a direct angle of attack readout should be visible to pilots
  • Referring to the pilot flying's initial "destabilising" sidestick input, the report states: "It is worth noting that the inputs applied to a sidestick by one pilot cannot be observed easily by the other one." However, the BEA says, the pitch-up manoeuvre was not queried by the pilot not flying (PNF). It adds: "Identification of the failure appeared to become a priority over control and flightpath monitoring. Consequently, he [the PNF] was unaware of the climb."

Asked for guidance on its policy following publication of the BEA report, Airbus provided information to Flightglobal which included these statements: "Improvements in safety are not achieved easily. Any change brings with it the risk of additional complexity, impact on other systems and new procedures which may themselves become the cause of new events. Therefore, any possible changes must be thought about carefully and then fully discussed with all involved parties.

"Airbus will use its considerable engineering and flight operations expertise in pursuing each and every one of the recommendations made in the BEA report and then decide what, if any, decisions are justified as being beneficial and which will further increase the level of safety already designed into the associated systems."